/* 重置样式 */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.top-nav {
  background: #ff0000;
  col or: #ff0000;
  display: flex;
  align-items: center;
}

.top-nav ul {
  list-style-type: none;
  display: flex;
}

.top-nav ul li {
  padding: 10px 20px;
  cursor: pointer;
  position: relative;
}

.dropdown-menu {
  display: none;
  position: absolute;
  background-color: #ff0000;
  border: 1px solid #ff0000;
  list-style-type: none;
  top: 100%;
  left: 0;
}

.dropdown-menu li {
  padding: 5px 10px;
  border-bottom: 1px solid #ccc;
}

.dropdown:hover.dropdown-menu {
  display: block;
}

.left-sidebar {
  width: 200px;
  height: 400px;
  border: 1px solid #ff0000;
  margin-top: 10px;
}